Seeing an outdoor scene in the reflections of my objects while in "material preview" mode but not in "rendered" mode?
Material preview uses a hidden HDRI to provide lighting and reflections. If you want your own lighting in Material Preview, click the little down arrow next to the preview mode &quot;circles&quot; to open the Viewport Shading options menu, and check &quot;scene lights&quot; and &quot;scene world&quot;.
Material preview also uses a renderer much the same as EEVEE to allow for fast previews of your materials, however you are using Cycles for your main render. Things such as transparency are handled differently in this mode, hence why your glass looks &quot;strange&quot;.